Rotor and method of forming

ABSTRACT

A rotor casting includes a lamination stack and a cast structure including proximal and distal cast end rings respectively adjacent proximal and distal end faces of the lamination stack. Cast axial ribs are distributed radially on a peripheral surface of the lamination stack and extend between the proximal and distal cast end rings. Cast feed members extend axially from the proximal cast end ring and are respectively positioned radially between an adjacent pair of axial ribs. In one example, cast bar segments integral to the proximal and distal cast end rings are formed in axial slots of the lamination stack. In one example, a bar insert in each axial slot has insert ends that extend respectively from the proximal and distal end faces of the lamination stack and are fully encapsulated respectively in the proximal and distal cast end rings. A method of forming the rotor casting is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/975,310, filed Apr. 4, 2014, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The disclosure relates to a rotor and a method of forming the rotor.

BACKGROUND

Electromagnetic machines such as electric motors, generators, andtraction motors are useful for converting energy from one form toanother. Such electromagnetic machines often include an elementrotatable about an axis of rotation. The rotatable element or rotor maybe coaxial with a static element or stator, and energy may be convertedvia relative rotation between the rotor and stator.

One type of electromagnetic machine, an alternating current inductionmotor, uses induced current flow to magnetize portions of the rotorduring motor operation. More specifically, the rotor may be composed ofa stack of steel laminations including teeth shaped to form poles anddefine slots therebetween. The poles may be separated by conductor barsdisposed in the slots and electrically connected to shorting ringslocated at opposing ends of the lamination stack. Induced current mayflow through the conductor bars which are disposed parallel to the axisof rotation along a periphery of the rotor. Each conductor bar may beelectrically connected to every other conductor bar by the two shortingrings disposed at opposite ends of the rotor. The interaction ofcurrents flowing in the conductor bars of the rotor winding and thestator's rotating magnetic field generates torque.

SUMMARY

A method of forming a rotor casting includes inserting a laminationstack defining a plurality of axial slots into a die cavity having adouble gating system including a plurality of feeder gates and aplurality of side gates, and providing molten material via the feedergates to the die cavity. The molten material flows from the feeder gatesvia a first cast ring element to the plurality of side gates and theperiphery of the lamination stack and via the side gates to a secondcast ring element and the periphery of the lamination stack to form acast structure of the rotor casting. The cast structure of the rotorcasting includes the first and second cast ring elements formed atopposing ends of the lamination stack, a plurality of cast ribs formedin the side gates and distributed radially on the periphery of thelamination stack, and a cast skin formed between the periphery of thelamination stack and the die cavity and extending between the cast ribsand into the slot openings to substantially encapsulate the periphery ofthe lamination stack in the cast material. The cast structure furtherincludes a plurality of cast feed members defined by the feeder gatesand subsequently removed from the rotor casting.

In one example, conductor bars are formed in the rotor casting bycasting cast bar segments in the slots of the lamination stack. In thisexample, the lamination stack is inserted into the die cavity such thatmolten material flows into the slots of the lamination stack via theslot openings at the opposing ends of the lamination stack from the castring elements and via the axial slot openings at the periphery of thelamination stack from the side gates to form a plurality of cast barsegments which form the conductor bars of the rotor assembly.

In another example, the conductor bars of the rotor assembly comprise aplurality of bar inserts which are inserted into the slots of thelamination stack prior to casting, such that opposing bar ends of eachbar insert extend respectively from opposing ends of the laminationstack. The lamination pack including the lamination stack and barinserts is inserted in the die cavity and the rotor casting is formedsuch that the opposing bar ends are overcast by the respective cast ringelement at each rotor end to form the conductor bars of the rotorassembly. In one example, a bar end of the insert bar defines a holethrough which molten material flows during the casting operation tofacilitate molten material flow during casting of the cast ring elementand minimize or substantially eliminate porosity formation duringcasting of the cast ring element.

A rotor assembly is also disclosed, the rotor assembly being formed byremoving material from the periphery of the rotor casting to define afinished surface of the rotor assembly.

The above features and advantages and other features and advantages ofthe present disclosure will be readily apparent from the followingdetailed description of the preferred embodiments and best modes forcarrying out the present disclosure when taken in connection with theaccompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a perspective view of a rotorcasting;

FIG. 2 is a schematic illustration of a perspective view of a rotorassembly formed from the rotor casting of FIG. 1;

FIG. 3 is a schematic illustration of a plan view of a firstconfiguration of a conductor bar insert;

FIG. 4 is a schematic illustration of a perspective view of a firstexample configuration of a lamination pack including the conductor barsinserts of FIG. 3 inserted into a lamination stack in preparation forforming the rotor casting of FIG. 1;

FIG. 5 is a schematic illustration of a perspective view of a caststructure of a first example configuration of the rotor casting of FIG.1, shown without the cast peripheral skin for clarity of illustration;

FIG. 6 is a schematic cross-sectional view of section A-A of the firstexample configuration of the rotor casting of FIG. 1 including thelamination pack of FIG. 4;

FIG. 7 is a schematic cross-sectional view of section B-B of the firstexample configuration of the rotor casting of FIG. 1 including thelamination pack of FIG. 4;

FIG. 8 is a schematic illustration of a plan view of a secondconfiguration of a conductor bar insert;

FIG. 9 is a schematic illustration of a cross-sectional view of sectionB-B of a second example configuration of the rotor casting of FIG. 1including a lamination pack including the conductor bar inserts of FIG.8 inserted into a lamination stack;

FIG. 10 is a schematic illustration of a cross-sectional view of sectionB-B of the first example configuration rotor casting of FIG. 1 showing abroken line corresponding to the finished surface of the rotor assemblyof FIG. 2;

FIG. 11 is a schematic cross-sectional view of section A-A of a thirdexample configuration the rotor casting of FIG. 1 including a laminationstack and cast conductor bar segments;

FIG. 12 is a schematic cross-sectional view of section B-B of the thirdexample configuration of the rotor casting of FIG. 1 including thelamination stack and cast conductor bar segments;

FIG. 13 is a schematic cross-sectional view of a casting die having adouble gate system including a plurality of feeder gates and a pluralityof side gates, showing a cross-sectional view of the lamination pack ofFIG. 4 including bar inserts and positioned in a die cavity of thecasting die during casting of the first example configuration of therotor casting of FIG. 1; and

FIG. 14 is a schematic cross-sectional view of the casting die of FIG.13 showing a cross-sectional view of a lamination stack positioned inthe die cavity during casting of the third example configuration of therotor casting of FIG. 1.

DETAILED DESCRIPTION

Referring to the Figures, wherein like reference numerals refer to likeelements, the elements shown in FIGS. 1-14 are not necessarily to scaleor proportion. Accordingly, the particular dimensions and applicationsprovided in the drawings presented herein are not to be consideredlimiting. A rotor casting 10 is shown generally in FIG. 1 and includes alamination stack 42 shown in FIG. 4 and a cast structure 14 showngenerally in FIG. 5. In a first example configuration, the rotor casting10 includes a lamination pack 16 shown generally in FIG. 4 and includinga plurality of bar inserts 54 shown generally in FIG. 3 which areinserted into slots 44 of the lamination stack 42 such that opposinginsert ends 56 of the bar insert 54 extend axially from respectiveopposing end faces 48, 148 of the lamination stack 42. The caststructure 14 includes opposing end cast ring elements 36, 136, aplurality of cast ribs 20, a cast peripheral skin 34 (shown in FIG. 1),and cast feed members 28. A cast ring element may also be referred toherein as a cast end ring. As shown in FIG. 1, the cast peripheral skin34 extends between adjacent ribs 20 such that the cast structure 14 atleast partially encapsulates a peripheral surface 66 of the laminationstack 42. Each of the cast ring elements 36, 136 includes an inner rim88 which extends over a respective end face 48, 148 of the laminationstack 42 to constrain axial movement of lamination stack 42 relative tothe cast structure 14. A rotor assembly 40 shown generally in FIG. 2 isformed by removing material from the rotor casting 10 of FIG. 1 to forma finished surface 90, for example, by machining or turning the rotorcasting 10 to remove, for example, the cast ribs 20 and cast peripheralskin 34. The rotor assembly 40 may be useful as a component of anelectromagnetic machine (not shown) for automotive applications, such asan alternating current induction motor. However, the rotor assembly 40may also be useful for non-automotive applications, including as acomponent of generators and electric motors for residential andcommercial applications.

By way of general explanation and described with reference to FIG. 1,the rotor assembly 40 may be rotatable about an axis 12 and may rotatewith respect to a stationary stator (not shown) of the electromagneticmachine (not shown). The axis 12 may also be referred to herein as anaxis 12 of rotation and may also be used to refer to the longitudinalaxis 12 of the various components of the rotor casting 10 including thelamination stack 42, the lamination pack 16, and the cast structure 14.For example, the axis 12 may be defined by a bore 18 extending throughthe axial length of the lamination pack 16. The rotor casting 10 and therotor assembly 40 formed therefrom has a first end shown generally at 32and which may be referred to herein as a proximal end 32, and furtherhas a second end opposing the first end 32 and shown generally at 132,which may be described herein as a distal end 132. For purposes ofillustration, in a non-limiting example the proximal end 32 of the rotorcasting 10 and rotor assembly 40 formed therefrom corresponds to thatend of the rotor casting 10 which is the end to which molten material 62flow (see FIGS. 13 and 14) is first introduced through a plurality offeeder gates 30 during the casting process forming the rotor casting 10,as described in further detail herein, e.g., the end of the rotorcasting 10 from which a plurality of cast feed members 28 extendsas-cast, as shown in FIG. 5.

The rotor casting 10 includes a lamination pack 16, shown in a firstexample configuration in FIG. 4. In the first example configurationshown in FIG. 4, the rotor casting 10 includes a lamination pack 16including the lamination stack 42 and the plurality of bar inserts 54(see FIG. 3) forming the conductor bars 52. In a second exampleconfiguration shown in FIG. 9, a rotor casting 100 includes thelamination pack 16 including the lamination stack 42 and a plurality ofbar inserts 154 (see FIG. 8) forming the conductor bars 152. In a thirdexample configuration shown in FIG. 12, a rotor casting 110 includes thelamination stack 42, however the slots 44 of the lamination stack 42 areleft empty to receive molten material 62 during the casting process toform cast bar segments 70, e.g., in the third example configuration nobar inserts are inserted into the lamination stack 42 prior to casting.Further, as shown in FIG. 11, in the third example configuration thecast ring elements 36, 136 of the rotor casting 110 are formed only ofmolten material 62 such that cast bar segments 70 and cast ring elements36, 136 are cast simultaneously and are unitary with each other andintegral to the cast structure 14. The cast ring elements 36, 136 andthe cast bar segments 70 are thus electrically connected with oneanother.

The lamination stack 42 may be formed from a plurality of laminationsteels, which for clarity of illustration are not shown in detail in thefigures. More specifically, each of the plurality of lamination steelsmay be an individual annular layer (not shown) of lamination steel,e.g., silicon steel, and may be stacked adjacent another one of theplurality of lamination steels to form the lamination stack 42. Thelamination stack 42 may have bore 18 extending the axial length of thelamination stack 42, and include the proximal end face 48 and the distalend face 148 spaced apart from the proximal end face 48. The laminationstack 42 defines the plurality of slots 44 extending from the proximalend face 48 to the distal end face 148. That is, when the laminationsteels are stacked adjacent one another, each one of the individualannular lamination steels may align with every other one of theindividual lamination steels to define bore 18 and the plurality ofslots 44 spaced about the periphery 66 of the lamination stack 42. Theperiphery 66 may also be referred to herein as a peripheral surface 66.In one example, the plurality of slots 44 may extend through thelamination stack 42 parallel to the axis of rotation 12. Each slot 44may be configured to receive a bar insert 54 as shown in FIGS. 4 and 9.The examples provided herein are non-limiting. For example, although notshown, the lamination steels may be skewed relative to each other suchthat the plurality of slots 44 defined by the lamination stack 42 mayalso be arranged in a skewed configuration about the axis of rotation12. In another example not shown, bar inserts 54 may be inserted intothe plurality of slots 44 of the lamination stack 42, then thelamination steels may be skewed relative to each other such that theplurality of slots 44 and the bar inserts 54 inserted therein are alsoarranged in a skewed configuration about the axis of rotation 12.

Each slot 44 defines an axial slot opening 46 such that each slot 44 isopen to the periphery 66, e.g., the peripheral surface 66, of thelamination stack 42, such that during the casting operation, moltenmaterial 62 may enter the slot 44 via the axial slot opening 46. Eachslot 44 is open at either end of the lamination stack 42 such that eachslot 44 is open to the proximal and distal end 32, 132 faces of thelamination stack 42, and such that in the first and second exampleconfigurations shown in FIGS. 4 and 9 respectively, each slot 44 canreceive a bar insert 54, 154 inserted thereto, or alternatively, suchthat in the third example configuration shown in FIGS. 11 and 12, moltenmaterial 62 can flow into the slot 44 during the casting process via theslot openings 46 to form a cast bar segment 70.

The slots 44 defined by the lamination stack 42 are spaced equidistantlyabout the axis of rotation 12. The lamination stack 42 may include, forexample, from thirty (30) to one hundred fifty (150) slots 44, such thatafter assembly and casting the rotor casting 10 includes a plurality ofconductor bars 52 corresponding in number to the number of slots 44.Each conductor bar 52 is configured to conduct electrical current duringoperation of the electromagnetic machine (not shown). Therefore, eachconductor bar 52 is formed from an electrically-conductive material.

In the first and second example configurations of rotor castings 10, 100shown in FIGS. 4 and 9 respectively, each conductor bar 52, 152 isformed by a respective bar insert 54, 154, where each of the bar inserts54, 154 is formed of an electrically conductive material and is insertedinto a slot 44 in the lamination stack 42 prior to casting the rotorcasting 10. In the third example configuration of a rotor casting 110shown in FIG. 12, the cast material forming the cast bar segment 70 isan electrically conductive material. By way of non-limiting example, theelectrically conductive material forming the conductor bars 52, 152 maybe an aluminum-based material or a copper-based material.

Referring to the first example configuration shown in FIGS. 3 and 4, abar insert 54 includes opposing insert ends 56 and a bar central portion58 therebetween. Referring to FIGS. 3 and 4, the bar insert 54 of FIG. 3is inserted into each of the slots 44 of the lamination stack 42 asshown in FIG. 4 such that the central portion 58 of the bar insert 54 isdisposed adjacent and in direct contact with the lamination stack 42within the slot 44 and such that the opposing insert ends 56 of the barinsert 54 extend from, respectively, the distal and proximal end 132, 32faces of the lamination stack 42. That is, the bar insert 54 directlyabuts the lamination stack 42 within the slot 44 and is not separatedfrom the lamination stack 42 by, for example, a layer of varnish, acoating, a resin, and/or a separator. As shown in FIGS. 4 and 7, thecentral portion 58 of the bar insert 54 is fully contained in the slot44 and does not extend into the axial slot opening 46. In one example,the insert ends 56 of each bar insert 54 each define a hole 64 throughwhich molten material 62 flows during the casting operation tofacilitate molten material 62 flow in the cast ring element 36, 136 tominimize or substantially eliminate porosity formation in the cast ringelement 36, 136 during casting. In the example shown, the hole 64 isconfigured as an oval or round hole 64 such that the molten material 62flows through the hole 64 with little to no turbulence. The exampleshown is non-limiting, and other hole 64 configurations and shapes maybe used which provide for uniform and non-turbulent flow of the moltenmaterial 62 through the hole 64 around the insert end 56 to avoid theformation of porosity during the casting operation. By way ofnon-limiting example, the hole may be sized relative to the bar insert54 such that the cross-sectional area of the hole is less than thecross-sectional area of the insert end 56 extending from the end face48, 148 of the lamination pack 42. In the non-limiting example shown,the insert ends 56 are generally rectangular with squared off corners.Other configurations may be used, for example, the insert ends 56 mayhave chamfered or rounded edges or may be otherwise configured tocorrespond with the profile of the cast ring elements 36, 136 and/or theprofile of the finished shorting rings 60, 160, and such that the insertends 56 are fully encapsulated by the cast material forming the shortingrings 60, 160.

As shown in FIGS. 5, 6, 7 and 13, during casting of the rotor casting10, molten material 62 flows from the feeder gates 30 and side gates 24around the insert ends 56 and through the holes 64 defined by the insertends 56 to form the cast ring elements 36, 136, such that the insertends 56 are fully encapsulated in the cast ring elements 36, 136 toconstrain radial and axial movement of the bar inserts 54, 154 and thelamination stack 42, and to electrically connect the cast ring elements36, 136 and the bar inserts 54, 154 with one another. Inner rims 88defined by the proximal and distal cast ring 36, 136 elements are formedin contact with the proximal and distal end 32, 132 faces of thelamination stack 42 and extend radially inward from the periphery 66 ofthe lamination stack 42 to constrain axial movement of the laminationstack 42. Further, as shown in FIGS. 5, 6, 7 and 13, molten material 62flows through the side gates 24 and between the periphery 66 of thelamination stack 42 and the surface of a die cavity 74 to form castaxial ribs 20 and a peripheral skin 34 which extends between the axialribs 20 and into the slot openings 46 of the lamination stack 42 toencapsulate the periphery 66 of the lamination stack 42. By way ofexample, lamination stack 42 is positioned in the die cavity 74 suchthat a gap 106 between the periphery 66 of the lamination stack 42 andan adjacent peripheral surface 102 of the die cavity 74 is uniform aboutthe periphery 66 of the lamination stack 42, and such that the cast skin34 formed therebetween is of a uniform thickness. The uniform thicknessof the cast skin 34 facilitates removal of all or a portion of the skinthickness during finishing of the rotor casting 10 to form the rotorassembly 40, as described in further detail herein. By way ofnon-limiting example, the radial thickness of the cast skin 34 may beuniform and in the range of 0-2.0 mm, and may be nominally 1.0 mm inthickness. In one example, the rotor casting 10 shown in FIGS. 6-7 maybe formed with minimal or negligible skin 34, for example, byconfiguring the die cavity such that the periphery 66 of the laminationstack 42 is slip fit to the adjacent peripheral surface 102 of thesection of the die cavity 74 defined by a second die component 84 (seeFIG. 13), e.g. such that molten material 62 flowing through the sidegates 24 enters the side gates 24 through a proximal transition 26 andexits through a distal transition 126 of each side gate 24, and issubstantially constrained from flowing across the periphery 66 from theside gate 24, such that the resulting cast skin 34 may have a radialthickness in the range of 0-0.25 mm. In another example, the rotorcasting 100 shown in FIG. 9 may be formed with a cast skin 34 having aradial thickness substantially equal to the radial distance a bar tab 68extends from the periphery 66 of the lamination stack 42, such thatduring finished machining of the rotor casting 100, for example, byturning, the turning tool is in contact with and cutting a continuousperipheral surface including the cast skin 34 and bar tabs 68 tofacilitate a smooth cutting and forming the uniform finished surface 90.In one example, referring to the cast rotor 100 shown in FIG. 9, the bartab 68 may extend radially 0.1-0.25 mm from the periphery 66 of thelamination stack 42.

Referring to FIGS. 8 and 9, a second example configuration of a rotorcasting 100 is shown in FIG. 9 including the bar insert 154 shown inFIG. 8. The bar insert 154 includes opposing insert ends 56 and barcentral portion 58 therebetween. The bar insert 154 further includes thetab 68 extending the axial length of the central portion 58. Referringto FIGS. 8 and 9, a bar insert 154 of FIG. 8 is inserted into each ofthe slots 44 of the lamination stack 42 as shown in FIG. 9 such that thecentral portion 58 of the bar insert 54 is disposed adjacent and indirect contact with the lamination stack 42 within the slot 44 and suchthat the opposing insert ends 56 of the bar insert 54 extend from,respectively, the distal and proximal end 132, 32 faces of thelamination stack 42. That is, the bar insert 54 directly abuts thelamination stack 42 within the slot 44 and is not separated from thelamination stack 42 by, for example, a layer of varnish, a coating, aresin, and/or a separator. As shown in FIGS. 8 and 9, the tab 68 isconfigured such that when the bar insert 154 is inserted into the slot44, the tab 68 is positioned in the slot opening 46 as shown in FIG. 9.The tab 68 may extend radially into the slot opening 46 such that thetab 68 is flush with or extends radially outward from the periphery 66of the lamination stack 42. The tab 68 positioned in the slot opening 46may constrain radial movement of the bar insert 154 relative to the slot44 and/or constrain radial movement of the lamination sheets (not shown)relative to each other in the lamination stack 42. As shown in FIGS. 5,6, and 9 and with reference to FIG. 13, during casting of the rotorcasting 100, molten material 62 flows from the feeder gates 30 and sidegates 24 around the insert ends 56 and through the holes 64 defined bythe insert ends 56 to form the cast ring elements 36, 136, such that theinsert ends 56 are fully encapsulated in the cast ring elements 36, 136to constrain radial and axial movement of the bar inserts 54, 154 andthe lamination stack 42, and to electrically connect the cast ringelements 36, 136 and the bar inserts 54, 154 with one another. Innerrims 88 defined by the proximal and distal cast ring 36, 136 elementsare formed in contact with the proximal and distal end 32, 132 faces ofthe lamination stack 42 and extend radially inward from the periphery 66of the lamination stack 42 to constrain axial movement of the laminationstack 42. Further, as shown in FIGS. 5, 6, 9 and 13, molten material 62flows through the side gates 24 and between the periphery 66 of thelamination stack 42 and the surface of the die cavity 74 to form castaxial ribs 20 and a peripheral skin 34 which extends between the axialribs 20 and into the slot openings 46 of the lamination stack 42 and/orperipherally between the tabs 68 to encapsulate the periphery 66 of thelamination stack 42.

Each bar insert 54, 154 may be configured to conduct electrical currentduring operation of the electromagnetic machine (not shown). Therefore,each bar insert 54 may be formed from an electrically-conductivematerial. For example, each bar insert 54 may be formed from copper or acopper alloy such as a copper nickel alloy or a copper boron alloy.Advantageously, the bar insert 54, 154 may be formed from anelectrolytic tough pitch copper alloy, such as C110 copper alloy, orother electrically conductive alloy so that the rotor casting 10, 110 iseconomical to manufacture. As used herein, the terminology electrolytictough pitch copper alloy refers to a copper alloy including oxygen in anamount of from about 0.02 parts by volume to about 0.04 parts by volumebased on 100 parts by volume of the copper alloy. Alternatively, the barinsert 54 may be formed from an oxygen-free copper alloy, such as C102copper alloy. As used herein, the terminology oxygen-free copper alloyrefers to a copper alloy including oxygen in an amount of from about0.05 parts by volume to about 0.1 parts by volume based on 100 parts byvolume of the copper alloy. The example of a copper-containing barinsert 54, 154 is intended to be non-limiting, and the bar insert 54,154 may be made of any suitable electrically-conductive materialformable into a bar insert 54, 154 which may be overcast as describedherein. For example, the bar insert 54, 154 may be made of an aluminummetal alloy or other electrically conductive alloy which may be formedinto bar insert 54, 154 for insertion into a lamination stack 42 andwhich may be overcast by the method described herein to form a conductorbar 52, such that the conductor bars 52 formed by the bar inserts areelectrically connected to the cast ring elements 36, 136 and with oneanother in the rotor casting 10, 110.

Referring now to FIG. 10, shown is a cross-section of the rotor casting10 including a dashed line indicating the finished surface 90 of therotor assembly 40 relative to the rotor casting 10. The rotor assembly40 is formed from the rotor casting 10 by removing material from theperimeter of the rotor casting 10 to define the finished surface 90. Asshown in FIG. 10 and referring also to FIGS. 1 and 2, at least the castribs 20 and a substantial amount of the cast skin 34 extending betweenthe cast ribs 20 is removed to provide the finished surface 90. In oneexample, the “substantial amount of cast skin 34” removed from theperiphery 66 of the lamination stack 42 includes substantially all ofthe cast skin 34 on the outer diameter of the lamination steels formingthe lamination stack 42, however may exclude removal of the castmaterial present in the slot openings 46. By way of example, forming thefinished surface 90 may include removing all of the cast ribs 20 andcast skin 34 and additionally removing material from the peripheralsurface 66 of the lamination stack 42 including material in the slotopening 46 such that the conductor bars 52 are exposed at the periphery66 of the rotor assembly 40, as shown in FIG. 2 with reference to FIGS.4 and 10.

Additional machining and/or finishing may be performed on either or bothof the proximal and distal cast ring 36, 136 elements to finish formingthe respective proximal and distal shorting rings 60, 160 of the rotorassembly 40. It would be understood that the cast feed members 28 wouldbe removed from the rotor casting 10, either at time of casting orsubsequently, as a step in finishing the rotor casting 10 to provide therotor assembly 40. Removing the cast feed members 28 from the rotorcasting 10 may include machining or other finishing of the proximal end32 of the rotor casting 10 to form the proximal shorting ring 60.

Further, machining and/or finishing may be performed on the rotorassembly 40 to balance the rotor assembly 40. For example, additionalmaterial may be removed from one or more surfaces 66, 90 of the rotorassembly 40 such as the periphery 66 of the lamination pack 16 and/orsurfaces 66, 90 defined by the proximal and/or distal shorting rings 60,160 to balance the rotor assembly 40 about the axis of rotation 12.

A method of forming a rotor assembly 40 from a rotor casting 10, 100,110 includes forming the rotor casting 10, 100, 110 by positioninglamination stack 42 in die cavity 74 of a casting die 80. The die cavity74 defines a rotor casting 10 including proximal and distal cast endrings 36, 136 at opposing ends of the lamination stack 42, and flowingmolten material 62 into the die cavity 74 via a double gating systemincluding feeder gates 30 and side gates 24 defined by the casting die80, to form the rotor casting 10 including the lamination stack 42 andthe cast structure 14. The method may include stacking a plurality oflamination steels (not shown in detail) adjacent and in contact with oneanother to form the lamination stack 42. That is, as set forth above anddescribed with reference to FIG. 4, stacking may include forming thelamination stack 42 having the proximal end face 48 and the distal endface 148, and defining the bore 18 and plurality of slots 44 through thelamination stack 42 that extend from the proximal end face 48 to thedistal end face 148. The individual lamination steels may be stackedadjacent one another via any process. For example, each lamination steelmay first be individually stamped to define the bore 18 and thensubsequently stacked and pressed adjacent another lamination steel usinga mandrel 50. In the example shown in FIG. 13, and referring to thefirst and second example configurations of the rotor castings 110 shownin FIGS. 3-4 and 6-9, the method further includes inserting a pluralityof bar inserts 54 into the plurality of slots 44 of the lamination stack42 to form a lamination pack 16 as shown generally in FIG. 4 andpreviously described herein, prior to positioning the lamination pack 16in the die cavity 74.

In the example shown, the die cavity 74 includes a plurality of diecomponents 82, 84, 86 and includes and/or is configured to receive amandrel 50. The lamination stack 42 may be positioned on the mandrel 50to locate the lamination stack 42 relative to the die cavity 74. In oneexample and as shown in FIGS. 13 and 14, the mandrel 50 may beconfigured to interface with the bore 18 of the lamination stack 42. Inthe example shown, the casting die 80 includes a first, second and thirdcomponent 82, 84, 86, which may be interlocking or otherwise oriented toeach other relative to die 80 parting lines 78 to define the die cavity74. In the example shown, the first and third die components 82, 86define, respectively, the proximal and distal cast ring 36, 136 elementsof the rotor cast. Advantageously, the first and third die components82, 86 each include an aperture 76 for receiving the mandrel 50, suchthat the lamination stack 42 positioned on the mandrel 50 and theproximal and distal cast ring 36, 136 elements defined by the first andthird die components 82, 86 are each aligned to the axis 12 of themandrel 50 and to each other during casting of the rotor casting 10,100, 110 to facilitate balancing of the rotor assembly 40 duringsubsequent finishing and balancing operations performed on the rotorcasting 10, 100, 110.

The casting die 80 includes a plurality of feeder gates 30, each feedergate 30 extending from the proximal end 32 of the die cavity 74 and influid communication with the proximal end 32 of the die cavity 74 via apassage 72. In one example, the feeder gates 30 are distributed radiallyalong the die cavity 74 and relative to the axis 12 such that eachfeeder gate 30 is immediately adjacent the peripheral surface 102 of thedie cavity 74 and the periphery 66 of the lamination stack 42 positionedin the die cavity 74 to facilitate molten material 62 flow from thefeeder gates 30 into the gap 106 defined between the periphery 66 of thelamination stack 42 and the peripheral surface 102 of the die cavity 74adjacent the periphery 66. Further, each of the feeder gates 30 may beradially disposed between and in fluid communication with adjacent sidegates 24 to facilitate the flow of molten material 62 from the feedergates 30 into a plurality of side gates 24 defined by the die cavity 74.

The plurality of side gates 24 are disposed parallel to the axis 12 ofthe die cavity 74 and distributed radially along the peripheral surface102 of the die cavity 74 and adjacent the periphery 66 of the laminationstack 42 to form a plurality of axial ribs 20 distributed radially alongthe surface of the rotor casting 10, 100, 110 as shown, for example, inFIGS. 1 and 5-7. Each of the side gates 24 extends radially outward fromthe peripheral surface 102 of the die cavity and from a proximal end 32of the die cavity 74 to a distal end 132 of the die cavity 74, toprovide a side gate opening extending the axial length of the die cavity74. In the example shown, the first, second and third die components 82,84, 86 cooperate to define the side gates 24. By way of example andreferring to the rotor casting 10 and cast structure 14 shown in FIGS. 1and 5, and the casting die 80 shown in FIGS. 13 and 14, the first andthird die components 82, 86 define, respectively, a proximal and adistal transition 26, 126 of each side gate 24 configured to form,respectively, a cast proximal and a cast distal rib terminus 22, 122 ofthe ribs 20 of the rotor casting 10. The proximal and distal transitions26, 126 of the side gates 24 open, respectively, to the sections of thedie cavity 74 defining the proximal and distal cast ring elements 36,136, such that during the casting operation molten material 62 flowsthrough the proximal transition 26 into the intermediate section of theside gate 74, from the intermediate section of the side gate 74 intoslot openings 46 adjacent the side gate 74 and into the gap 106 betweenthe peripheral surface 102 and the periphery 66 of the lamination stack42 to form the cast skin 34, and from the distal transition 126 to thedistal end face 148 of the lamination stack 42 to form the distal castring element 136.

The second die component 84 defines the peripheral surface 102 of thedie cavity and partially defines an intermediate portion of each of theplurality of side gates 24 which are distributed radially along theperipheral surface 102. The intermediate portion of each side gate 24extends axially between the proximal and distal transitions 26, 126 ofthe respective side gate 24. Each side gate 24 is continuously open tothe die cavity 74 along the axial length of the die cavity 74, e.g.,from the proximal end 32 of the die cavity 74 to the distal end 132 ofthe die cavity 74. As such, with the lamination stack 42 positioned inthe die cavity 74 as shown in FIGS. 13 and 14, the opening of the sidegate 24 to the die cavity 74 extends continuously the axial length ofthe periphery 66 of the lamination stack 42, and such that duringcasting, molten material 62 flows from the opening of the side gate 24along the axial length of the die cavity 74 to form of each respectiveaxial rib 20. In the example shown, the portion of the side gate 24defined by the second die component 84 forms an intermediate portion 104of the axial rib 20 intermediate the proximal and distal rib terminus22, 122.

The first, second and third die components 82, 84, 86 are configured tointerlock and/or be aligned to each other to align the intermediatesection of each side gate 24 defined by the second component 84 with thecorresponding proximal and distal transitions 26, 126 defined by thefirst and third die components 82, 86. Each of the proximal and distaltransitions 26, 126 are tapered or otherwise similarly configured, forexample, with a chord geometry to define a transverse cross-sectionwhich gradually decreases in cross-sectional area from the transversecross-section of the intermediate portion 104 of the axial rib 20 to theterminating end of the respective proximal and distal rib terminus 22,122 to minimize turbulence in the molten material 62 as the moltenmaterial 62 flows between the second die component 84 and the first andthird die components 82, 86, while directing flow of the molten material62 in the die cavity 74 during the casting operation to minimize and/orsubstantially eliminate porosity in the rotor casting 10, and inparticular in the cast ring elements 36, 136. The cast distal andproximal rib terminus 122, 22 are tapered and/or similarly configured togradually decrease in cross-sectional area from the transversecross-section of the intermediate portion 104 of the rib 20 to therespective proximal and distal ends 32, 132 of the rotor casting 10,which is advantageous to finishing of the cast ring elements 36, 136 toform the shorting rings 60, 160, for example, by reducing the amount ofmaterial which must be removed to finish the shorting rings 60, 160.

Each of the side gates 24 may be characterized by a transversecross-section that is generally semicircular in shape, as shown in FIGS.5-7, to facilitate smooth, non-turbulent flow of the molten material 62through the side gate, minimizing formation of porosity and die wear.Additionally the semicircular cross-section is easily and economicallyformed in the casting die 80, thus reducing die fabrication costs. Thenumber and size of side gates 24 defined by the die cavity 74 may beconfigured to correspond and/or be relative to the size and/or volume ofthe cast ring elements 36, 136 and/or to correspond to the configurationand arrangement of the slots 44 in the lamination stack 42. By way ofnon-limiting example, the size and shape of the transverse cross-sectionof each the side gates 24 may be configured such that, as shown in FIG.7, each gate overlaps, e.g., is directly adjacent, two consecutive slotopenings 46 of the lamination stack 42, such that molten metal 62flowing from the side gate 24 flows onto the periphery 66 between and oneither side of the two consecutive slot openings 46 to form the castskin 34, and, in the example of the rotor casting 110 shown in FIG. 12,into the slots 44 through the slot openings 46 to form the cast barsegments of the rotor casting 110. In one example, the number of sidegates 24 and the transverse cross-sectional area of each side gate 24may be related to the transverse cross-sectional area of each of thecast ring elements 36, 136, to ensure sufficient flow of molten material62 through the side gates 24 to form the cast structure 14, and to formthe distal cast ring element 136. The number of side gates 24 and thetransverse cross-sectional area of each side gate 24 may be configuredsuch that the total cross-sectional area of the plurality of side gates24 is greater than the transverse cross-sectional area of the cast ringelement 136, by a factor in the range of 1-1.5. For example, where thecross-sectional area of the distal cast ring element 136 is A mm², andthe cross-sectional area of each of the side gates 24 is B mm2, then therequired number of side gates 24 each having a cross-sectional area of Bmm² may be determined as N>A|B, where N is the required number of sidegates. Alternatively, where the number N of side gates 24 has beenestablished, for example, to provide a sufficient number N of side gates24 to align each of the side gates 24 with at least to slots 44 of thelamination stack 42, the minimum required cross-sectional area B of eachof the side gates 24 may be determined as B>A|N. The examples providedherein are non-limiting, and it would be understood that otherconfigurations, e.g., number, size and shape, of the side gates 24 maybe used which provide sufficient axial flow of molten material 62 in thedie cavity 74 to form the distal cast ring element 136.

The method includes introducing molten material 62 into the die cavity74 via an inlet 38 and through a plurality of feeder gates 30 andflowing the molten material 62 into the proximal end 32 of the diecavity 74 via the plurality of feeder gates 30 and passages 72 fluidlyconnecting the feeder gates 30 to the die cavity 74. The molten material62 represented by arrows in FIGS. 13 and 14 flows through the die cavity74 and side gates 24 as shown in FIGS. 13 and 14 to form, respectively,the cast structure 14 of the rotor castings 10, 100. By way ofnon-limiting example, in the configuration shown in FIG. 13, the moltenmaterial 62 may be one of a copper alloy and an aluminum alloy. Theexamples provided herein are non-limiting, such that the molten material62 may be any flowable, castable electrically conducting material. Themolten material 62 flows from the feeder gates 30 into the first diecomponent 82 and fills the section of the die cavity 74 defined by thefirst component 82 to form the proximal cast ring element 36 whilequickly flowing through the proximal transitions of the respective sidegates 24 and between the periphery 66 of the lamination stack 42 and thesecond die component 84 to form the cast skin 34 on the periphery 66 ofthe lamination stack 42 adjacent the proximal end 32 of the laminationstack 42. The molten material 62 flows from the proximal transition 26through the side gates 24 to the distal transition 126 and into thethird die component 86 to form the distal cast ring 136 element, andthrough the side gates 24 between the periphery 66 of the laminationstack 42 and the second die component 84 and, as shown for rotorcastings 10, 110, into the slot openings 46 to form the cast skin 34between the cast ribs 20 which are formed in the side gates 24.

Referring to the first and second example configurations shown in FIGS.4-9 of a rotor casting 10, 100 including respective bar inserts 54, 154inserted into the lamination stack 42 to define the conductor bars 52 ofthe rotor assembly 40 formed therefrom, and referring to the die cavity74 of FIG. 13 showing a lamination pack 16 including the bar inserts 54positioned in the die cavity 74, the method of casting the rotor casting10, 100 includes the molten material 62 flowing from the feeder gate 30into section of the die cavity 74 defined by the first die component 82and proximal transitions of the side gates 24, and from the proximaltransitions through the intermediate sections and distal transitions ofthe side gates 24 into the section of the die cavity 74 defined by thirddie component 86 to form, respectively, the proximal and distal castring 36, 136 elements. During forming of the cast end ring elements 36,136, the molten material 62 quickly flows around the insert ends 56 andthrough the holes 64 in the insert ends 56 such that the molten material62 in the cast ring elements 36, 136 solidifies uniformly and withminimal or substantially no porosity, such that the interface betweenthe insert end 56 and the cast end ring element 36, 136 is absent ofporosity or other solidification discontinuities such as cracks or foldswhich may affect the integrity of the electrical connection between theinsert end 56 and the cast end ring element 36, 136. Concurrently withforming the cast ring elements 36, 136, the molten material 62 flowsfrom the section of the die cavity 74 defined by the first die component82 and from the side gates 24 between the periphery 66 of the laminationstack 42 and the second die component 84 to form the cast skin 34 on theperiphery 66 of the lamination stack 42, where forming the cast skin 34may include flowing molten metal 62 into the slot opening 46 adjacentthe bar insert 54, for example, as shown in FIG. 7.

Referring to the third example configuration shown in FIGS. 11 and 12 ofa rotor casting 110 including integrally cast bar segments 70 definingthe conductor bars 52 of a rotor assembly 140 formed therefrom, andreferring to the die cavity 74 of FIG. 14 showing the lamination stack42 positioned in the die cavity 74 such that the empty slots 44 of thelamination stack 42 are in fluid communication with the die cavity 74,the method of casting the rotor casting 110 includes flowing the moltenmaterial 62 from the feeder gate 30 into section of the die cavity 74defined by the first die component 82 to form the proximal cast ringelement 36, and flowing molten metal 62 via the proximal cast ringelement 36 through the proximal transitions of the side gates 24 intointermediate sections and distal transitions of the side gates 24 suchthat molten metal 62 flows through the side gates to the section of thedie cavity 74 defined by third die component 86 to form the distal castring 136 elements. Concurrently with forming the cast ring elements 36,136, the molten material 62 flows from the section of the die cavity 74defined by the first die component 82 and from the side gates 24 betweenthe periphery 66 of the lamination stack 42 and the second die component84 into the slots 44 via the slot openings 46 on the periphery 66 andproximal end face 48 of the lamination stack 42 to form the cast barsegments 70, and to form the cast skin 34 on the periphery 66 of thelamination stack 42, for example, as shown in FIG. 12. The moltenmaterial 62 may cool and solidify in the slots 44 faster than the moltenmaterial 62 in the side gates 24, due to, for example, the smallerrelative cross-sectional area and larger relative surface to volumeratio of the slot relative to the side gate, such that the distal castring element 136 may be formed substantially of molten material 62flowing into the section of the die cavity 74 defined by the third diecomponent 86 via the side gates 24. The molten material 62 in the castring elements 36, 136 and in the cast bar segments 70 formed in theslots 44 of the lamination stack 42 solidifies uniformly and withminimal or substantially no porosity, such that the cast bar segments 70and the cast ring elements 36, 136 and the interface therebetween isabsent of porosity or other solidification related discontinuities suchas cracks or folds which may affect the integrity of the electricalconnection between the cast bar segments 70 defining the conductor bars52 of the rotor casting 110 and the cast ring elements 36, 136 of therotor casting 110.

The molten material 62 solidifies in the die cavity 74 to form the caststructure 14 of the rotor casting 10, 100, 110, and the rotor casting10, 100, 110 is removed from the die cavity 74 and casting die 80. Asdescribed previously herein, the finishing operations are performed onthe rotor casting 10, 100, 110 to form the rotor assembly 40, includingremoving material from the perimeter of the rotor casting 10 to definethe finished surface 90. By way of example, forming the finished surface90 may include removing all of the cast ribs 20 and cast skin 34 andadditionally removing material from the peripheral surface 66 of thelamination stack 42 including material in the slot opening 46 such thatthe conductor bars 52 are exposed at the periphery 66 of the rotorassembly 40, as shown in FIG. 2 with reference to FIGS. 4 and 10.

Additional machining and/or finishing may be performed on either or bothof the proximal and distal cast ring 36, 136 elements to finish formingthe respective proximal and distal shorting rings 60, 160 of the rotorassembly 40. It would be understood that the cast feed members 28 wouldbe removed from the rotor casting 10, 100, 110, either at time ofcasting or subsequently, as a step in finishing the rotor casting 10 toprovide the rotor assembly 40. Removing the cast feed members 28 fromthe rotor casting 10, 100, 110 may include machining or other finishingof the proximal end 32 of the rotor casting 10, 100, 110 to form theproximal shorting ring 60. Further, machining and/or finishing may beperformed on the rotor assembly 40 to balance the rotor assembly 40. Forexample, additional material may be removed from one or more surfaces66, 90 of the rotor assembly 40 such as the periphery 66 of thelamination pack 16 and/or surfaces 66, 90 defined by the proximal and/ordistal shorting rings 60, 160 to balance the rotor assembly 40 about theaxis of rotation 12.

The reduced porosity of the cast structure 14 provided by the castingmethod described herein improves electrical conductivity and simplifiesrotor balancing of the rotor assembly 40 formed from the rotor casting10, 100, 110, which may significantly improve electrical and mechanicalperformance of the rotor assembly 40. In addition, the rotors formed bythe method exhibit excellent electrical conductivity and efficiencyduring operation which may be attributed to direct contact between theend of each conductor bar 52 and the cast ring elements 36, 136 formingthe shorting rings 60, 160. In particular, the method forms a strongjoint between the plurality of conductor bars 52 and the cast ringelements 36, 136 forming the shorting rings 60, 160 that can adequatelywithstand inertial forces during rotor operation. As such, the rotorassemblies 40 formed by the method are useful for applications requiringelectromagnetic devices (not shown) having excellent power density.

While the best modes for carrying out the disclosure have been describedin detail, those familiar with the art to which this disclosure relateswill recognize various alternative designs and embodiments forpracticing the disclosure within the scope of the appended claims.

1. A rotor casting comprising: a lamination stack having a proximal endface and a distal end face; an axis of rotation defined by thelamination stack; a cast structure comprising: a proximal cast end ringadjacent the proximal end face; a distal cast end ring adjacent thedistal end face; and a plurality of axial ribs distributed radially on aperipheral surface of the lamination stack relative to the axis ofrotation; wherein each of the plurality of axial ribs extends betweenthe proximal cast end ring and the distal cast end ring.
 2. The rotorcasting of claim 1, further comprising: a plurality of axial slotsdefined by the lamination stack and distributed radially on theperiphery of the lamination stack relative to the axis of rotation; eachof the axial slots extending between the proximal and distal end faces;wherein the cast structure further comprises: a plurality of cast barsegments formed in the plurality of slots of the lamination pack, eachof the cast bar segments extending between and integral to the proximaland distal cast end rings.
 3. The rotor casting of claim 1, furthercomprising: a cast peripheral skin extending from the plurality of axialribs to at least partially encapsulate the peripheral surface of thelamination stack.
 4. The rotor casting of claim 3, wherein each of theaxial ribs extends radially from the cast peripheral skin.
 5. The rotorcasting of claim 1, further comprising: a plurality of cast feed membersextending axially from the proximal cast end ring.
 6. The rotor castingof claim 5, wherein the plurality of cast feed members are distributedradially on the proximal cast end ring.
 7. The rotor casting of claim 5,wherein each respective cast feed member is positioned radially betweena respective adjacent pair of axial ribs.
 8. The rotor casting of claim1, wherein each respective axial rib includes a distal rib terminusextending radially from the distal cast end ring and a proximal ribterminus extending radially from the proximal rib terminus.
 9. The rotorcasting of claim 1, further comprising: a plurality of axial slotsdefined by the lamination stack and distributed radially on theperiphery of the lamination stack relative to the axis of rotation; eachof the axial slots extending between the proximal and distal end faces;a bar insert disposed in each of the plurality of axial slots; whereineach bar insert includes first and second insert ends extendingrespectively from the proximal and distal end faces of the laminationstack.
 10. The rotor casting of claim 9, wherein the first insert endsare fully encapsulated in the proximal cast end ring and the secondinsert ends are fully encapsulated in the distal cast end ring.
 11. Therotor casting of claim 10, further comprising: wherein each of the firstand second insert ends defines a hole; wherein each respective hole isfilled with cast material of the cast structure.
 12. A method of forminga rotor casting, the method comprising: inserting a lamination stackinto a die cavity of a casting die; the lamination stack including: adistal end face and a proximal end face; an axis of rotation; and aplurality of axial slots distributed radially on a peripheral surface ofthe lamination stack relative to the axis of rotation and extendingbetween the proximal and distal end faces; the die cavity having aproximal end and a distal end; the die cavity defining a cast structureof the rotor casting including: a proximal cast end ring; a distal castend ring; a plurality of axial ribs distributed radially on theperipheral surface of the lamination stack and extending continuouslybetween the proximal and distal cast end rings.
 13. The method of claim12, further comprising: the casting die having a gating systemincluding: a plurality of side gates defined by the die cavity anddistributed radially relative to the longitudinal axis; each side gatedefining a continuous gate opening extending axially between theproximal and distal ends of the die cavity such that the side gateopening is immediately adjacent the periphery, distal end face andproximal end face of the lamination stack; the plurality of side gatesconfigured to flow molten material from the proximal end of the diecavity to the distal end of the die cavity and to form the plurality ofribs; the method further comprising: flowing molten material into thedie cavity via the plurality of side gates; and solidifying the moltenmaterial to form the cast structure of the rotor casting.
 14. The methodof claim 13, further comprising: the gating system including a pluralityof feeder gates distributed radially in fluid communication with theproximal end of the die cavity to receive the molten material into thedie cavity; the plurality of feeder gates in fluid communication withthe plurality of side gates; the method further comprising: flowingmolten material into the die cavity via the plurality of feeder gates.15. The method of claim 1, wherein the cast structure includes aplurality of cast bar segments formed in the plurality of axial slots ofthe lamination pack, each of the cast bar segments extending between andintegral to the proximal and distal cast ring elements.
 16. The methodof claim 1, further comprising: inserting a bar insert into each of theplurality of axial slots of the lamination stack prior to inserting thelamination stack into the die cavity; wherein each bar insert includesfirst and second insert ends extending respectively from the proximaland distal end faces of the lamination stack after insertion to thelamination stack; flowing molten material in contact with the first andsecond insert ends such that the first insert ends are fullyencapsulated in the proximal cast ring element and the second insertends are fully encapsulated in the distal cast ring element.
 17. Themethod of claim 16, wherein the first and second insert ends each definea hole; the method further comprising: flowing molten material throughthe hole during casting of the proximal and distal cast ring elements.18. The method of claim 16, further comprising: positioning thelamination stack in the die cavity to define a gap between theperipheral surface of the lamination stack and the die cavity; andflowing molten material into the gap to form a cast peripheral skin;wherein the cast peripheral skin at least partially encapsulates theperipheral surface of the lamination stack.